The multiple-input multiple-out-put (Multiple-Input Multiple-Out-put, MIMO) technology is an important breakthrough for signal processing technologies in the field of wireless communication, which implements high speed data transmission by introducing degree of freedom of spatial dimension. However, interference between signals is caused at the same time of improving the transmission rate, the interference is demonstrated as mutual interference between signals of antennas in a point-to-point single-user MIMO system, and the interference is not only demonstrated as mutual interference between signals of antennas, but also as mutual interference between signals of users in a point-to-multi-point multi-user MIMO system.
To improve the performance of the MIMO system, several precoding methods are put forward in the prior art for reducing the interference between signals. The main precoding methods are: BD (Block Diagonalization, block diagonalization), SZF (Successive zero-forcing), THP (Tomlison-Harashima), and DPC (dirty-paper coding). In implementation, a base station usually precodes downlink data sent to a user equipment by using a method which includes but is not limited to the foregoing methods. Generally, the base station needs to obtain channel state information of the user equipment for precoding. A method for feeding back frequency domain channel state information based on a group is usually adopted in a multi-user MIMO-OFDM (Orthogonal Frequency Division Multiplexing, orthogonal frequency division multiplexing) system to obtain channel state information of the user equipment, that is, several subcarriers of each OFDM symbol are divided into a group, for example, Ng connected subcarriers may be divided into a group, and the subcarriers of each OFDM symbol are divided into: Kg=┌k/Ng┐ groups in total, where k is the number of the subcarriers of each OFDM symbol. The user equipment needs to quantize only the channel state information of each group of the subcarriers, and send a codebook index corresponding to the quantized channel state information of each group of the subcarriers to the base station; however, in this way, the overhead of the codebook index to be sent for each OFDM symbol of each user equipment is as high as Kg bits.